set default environment variables in the CI

.github/workflows/ci.yml

@@ -205,7 +205,7 @@ jobs:
       env:
         ALPAKA_CI_OS_NAME: ${{runner.os}}
       shell: bash
-      run: cd ${GITHUB_WORKSPACE} && ./script/ci.sh
+      run: cd ${GITHUB_WORKSPACE} && source ./script/set_default_env_vars.sh && ./script/ci.sh
     - name: build + test
       if: (runner.os == 'Linux' || runner.os == 'macOS')
       env:

script/job_generator/generate_job_yaml.py

@@ -481,6 +481,7 @@ def create_job(job: Dict[str, Tuple[str, str]], container_version: float, gitlab
     job_yaml["image"] = job_image(job, container_version, gitlab_images)
     job_yaml["variables"] = job_variables(job)
     job_yaml["script"] = [
+        "source ./script/set_default_env_vars.sh",
         "source ./script/gitlabci/print_env.sh",
         "source ./script/gitlab_ci_run.sh",
     ]

script/run_generate.sh

@@ -21,15 +21,25 @@ echo_green "<SCRIPT: run_generate>"
 #
 # @param $1 cmake/environment variable name
 #
-# @result if $1 exists cmake variable definition else nothing is returned
+# @result if $1 exists cmake variable definition else nothing is returned. If variable is not
+# defined, the script will be exited.
 #
 # @code{.bash}
 # FOO=ON
+# BAR=""
 # echo "$(env2cmake FOO)" # returns "-DFOO=ON"
 # echo "$(env2cmake BAR)" # returns nothing
+# echo "$(env2cmake FOOBAR)" # exit 1
 # @endcode
 function env2cmake()
 {
+    # check if variable is defined
+    # TODO(SimeonEhrig): bring me back before merge
+    # if [ -z ${!1+x} ]; then 
+    #     kill -SIGTERM $$
+    # fi
+
+    # return only content of variable is not empty
     if [ ! -z "${!1}" ] ; then
         echo -n "-D$1=${!1}"
     fi

script/set_default_env_vars.sh

@@ -0,0 +1,5 @@
+#/usr/bin/env bash
+
+# set default values for unset environment variables
+
+export CMAKE_CXX_EXTENSIONS=${CMAKE_CXX_EXTENSIONS:="ON"}